Various techniques for carrying out the separation of HF and chlorofluorinated hydrocarbons have already been described. There may be mentioned, for example:
- U.S. Pat. No. 2,640,086, which relates to the separation of HF and chlorodifluoromethane and uses chloroform to promote the separation into two phases, a phase which is rich in HF and a phase which is poor in HF;
- U.S. Pat. No. 3,873,629, which relates to a continuous process for the separation of HF and chlorodifluoromethane and which consists in bringing the gaseous mixture of the two constituents into countercurrent contact with sulphuric acid;
- U.S. Pat. No. 3,976,447, which proposes separation of HF from gaseous effluents by absorption/desorption on particles of calcium, barium or strontium chloride;
- U.S. Pat. No. 4,209,470, which describes a process for the separation of HF from its mixtures with 1-chloro-1,1-difluoroethane to which, to improve the separation, is added a secondary liquid consisting entirely or largely of 1,1-dichloro-1-fluoroethane;
- U.S. patent application No. 0,353,970, which relates to the separation of HF from its mixtures with 2,2-dichloro-1,1,1-trifluoroethane and/or 2-chloro-1,1,1,2-tetrafluoroethane by settling and distillation.
In the case of mixtures of HF and F133a, a simple distillation does not make it possible to separate them because HF and F133a form an azeotrope which is more volatile than HF or F133a; the HF content of this azeotrope is approximately 60 molar % (20% by weight). At room temperature and whatever the concentrations of HF and F133a, the mixtures of HF and F133a do not separate into two phases.
On the other hand, it is possible to obtain an excellent separation of a mixture of HF and F133a provided that it is cooled to a temperature below 0.degree. C., preferably of between -40.degree. C. and -10.degree. C. It has also been found that it is possible to further improve this separation if the settling of HF and F133a is carried out in the presence of trichloroethylene (TCE).
The presence of TCE in the mixture of F133a and HF substantially reduces the solubilities of HF in the organic phase and of the organics in the HF phase; the separation of F133a and HF is thus carried out more efficiently.